This application relates in general to optical disc storage media and in particular to a mechanism for detecting fragmentation on rewritable optical disc media.
The files on randomly accessible data storage devices, such as hard drives and rewritable compact discs (CD-RW) become fragmented with use. As files are edited, deleted or added, portions of a file become separated from the remainder of the file. This causes or forms bole locations in the media that are not useand This will slow down system performance because of increased seek times for the system.
Note that normal compact disc (CD) write operations accelerate fragmentation. The CD disc is large when compared to the user data stored thereon, and the CD media have direct overwrite (DOW) limitations. Thus, the CD device will stagger the placement of data onto the disc. In other words when a file is edited, the older file or portion of the file is not overwritten, but rather the edited portion is written elsewhere on the disc, typically further downstream on the disc. Typical CD write and erase operations move data in a continuous loop from the front of the disc to the back of the disc to write data evenly across the disc. This reduces the wearout of the disc, but increases fragmentation as portions of the file are scatted across the disc.
In the prior art, programs are available to defragment hard drives or hard disks. A user would install and execute a program which would examine the disk and determine how the files are scattered across it. By copying files from their current location to other portions of the disk, and then filling in holes in the disks, the program is able to compact the files to the front end of the disk. Having all the files compactly located in the front of the disk, rather than scattered throughout the whole disk, decreases access time, and thus increases performance.
However, the hard drive defragmentation programs are not optimized for optical discs, such as CD-RW or digital versatile discs (DVD) rewrittable discs. Unlike hard drives, optical disc media, such as CD-RW media have very limited number of direct overwrites (DOW). CD-RW media can currently be overwritten about 1000 times before the disc wears out, whereas hard drives can be overwritten millions of times. The hard drive defragmentation programs that write and rewrite data several times to perform one defragmentation of the hard disk if applied to the CD technology would quickly wear out CD-RW discs. Also note that the file structure of a hard drive is different from that of a CD, a CD-RW, a DVD disc, or a DVD rewrittable disc. Furthermore, hard drive programs concentrate the data that is stored in the hard disk to one particular location, namely towards the inner diameter of the disk. Thus, hard drive programs would wear out the inner diameter of a CD disc before the rest of the disc.
If defragmentation is not performed on a disc, then performance will be degraded. Note that access time is even more critical for CDs than for hard drives. The access time for a typical hard disk is about 5 milliseconds, which is the time required for the head to swing halfway across the disk. The typical access time on CD-RW media is on the order of 150 milliseconds. The slower the device, the greater impact fragmentation has on performance, i.e. a 10% increase in access time on a CD is more pronounced than a 10% increase for a hard disk. Thus, defragmenting the CD disc would greatly improve system performance.
Another problem is that users do not know when to run the defragmentation programs on the hard disk. Users may not even be aware of defragmentation programs. Thus, users either run the program too frequently or too infrequently. If the user runs the program too frequently on hard drives, then this will have little effect on the hard drive because of the extremely high DOW. On the other hand, if this technology is applied to CDs, then a user rig the program too frequently will quickly wear out the CD disc. If the users run the program too infrequently on hard drives, then this will have a small effect on the performance of the hard drive because of the fast access times. On the other hand, if this technology is applied to CDs, then a user running the program too infrequently will suffer a large performance degradation because of the slow access time. The prior art does not automatically inform users of when to run defragmentation programs.
Thus, the prior art hard drive defragmentation programs are insufficient for use with optical disc technology, such as CD technology. Therefore, there is a need in the art for a defragmentation program that will automatically perform defragmentation when appropriate, which balances the DOW limitations with the performance gains yielded from defragmentation.
These and other objects, features and technical advantages are achieved by a system and method which implements a defragmentation utility on an optical disc, such as a CD-RW disc, a DVD rewrittable disc, or the like. Processing according to embodiments of the present invention is automatically invoked, and begins to examine the CD disc upon its insertion. This is preferably done in the background when no other user requested actions are pending. In the preferred embodiment, the examination will be interrupted if a user action is requested and then continue when the user action is complete, so the user will not experience any performance degradation. Processing according to embodiments of the present invention then determines the amount of fragmentation that the CD-RW disc has incurred through its use. This is determined by comparing an ideal data transfer time with a calculated amount of data transfer time. Transfer time depends on the amount of fragmentation (which effects access time) and the size of the file. If the amount of fragmentation exceeds a predetermined limit, then the disc is defragmented. In the preferred embodiment, the predetermined limit is a performance increase of greater than 25%, after defragmentation, for data retrieval times of greater than or equal to 10 seconds; a performance increase of greater than 10%, after defragmentation, for data retrieval times of greater than 1 second and less than 10 seconds. For data retrieval times of 1 second or less, preferably no defragmentation is performed.
The threshold limit represents a balance between CD performance and DOW requirements. During defragmentation, data from the CD disc is collected and stored on another storage medium, e.g. a hard disk. By using a storage medium separate from the CD disc for temporary storage, additional writes to the disc ate avoided. The data is then reorganized and written back to the CD disc.
Therefore, it is a technical advantage of the present invention to defragment optical discs, which improves performance of systems using optical discs.
It is another technical advantage of the present invention that the determination to defragment an optical disc, such as a CD-RW disc, balances the performance gains and DOW limitations.
It is a further technical advantage of the present invention that another storage media is used for temporary storage of data during defragmentation, which reduces the number of writes to the CD-RW disc.
It is a further technical advantage of the present invention that processing according to embodiments of the present invention operates in the background and is transparent to a user, thereby not interfering with the normal use of the CD-RW device.
It is a further technical advantage of the present invention that processing according to embodiments of the present invention automatically determines and performs defragmentation, thereby balancing performance and DOW.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.